Function Implementation

Trigger Conditions

The trigger condition for the optical line protection automatic switching is signal failure (SF), which includes the following conditions.

• The input power loss exceeds the threshold. The board-side alarm is LOS-MUT.
• The variance between primary and secondary input power exceeds the threshold. The board-side alarm is OPR-DIFF-OVER.

NOTE:

• The threshold of input power loss is -35 dBm by default.
• The variance threshold between primary and secondary input power is 5 dB by default.

Working Principle

The optical line adopts two pairs of fibers. One pair functions as the working route to transmit the service signals in normal cases. The other pair functions as the protection route to carry the protection signals when a fiber break occurs or the signal attenuation is too large.

This protection scheme adopts dual-fed signal selection and unidirectional switching. As shown in Figure 1 the RI1 and TO1 optical ports are connected by the working line fibers, and the RI2 and TO2 optical ports are connected by the protection line fibers.

For the description of the working principle of the OLP board, refer to the Hardware Description.

Figure 1 Working principle of optical line protection

: Direction of the working signal flow

: Direction of the protection signal flow

NOTE:

• The OTU is a transceiver and is able to process the receiving and transmitting of the optical signal at the same time. In Figure 1, the receiving OTU and the transmitting OTU in one station are physically one board.
• The OptiX OSN 6800A/8800 T16 (NA)/8800 T32 (NA)/8800 T64 (NA) and OptiX OSN 3800A support the same optical line protection in terms of working principle and application. The difference lies in that the OptiX OSN 6800A/8800 T16 (NA)/8800 T32 (NA)/8800 T64 (NA) uses the optical multiplexing/demultiplexing unit while the OptiX OSN 3800A uses the optical add/drop multiplexing unit.

• In the transmit direction, the multiplexed signals are input through the TI port. The OLP board sends the signals to the working line fiber through TO1 port and sends the signals to the protection line fiber through the TO2 port at the same time.
• In the receiving direction, the same two multiplexed signals are respectively received from the working line fiber and the protection line fiber. These signals are input through RI1 and RI2. The OLP detects and compares the optical power of the two signals and controls the protection switching of the working channel and the protection channel.
• In normal cases, the OLP sends the working signals from the RI1 port to the FIU board. When a LOS alarm of working channel occurs or when a OPR-DIFF-OVER alarm occurs, the OLP board sends the signals from the RI2 port to the FIU board. In this way, the line signals are automatically switched to the protection line fiber.
• After the recovery of the working line fiber, the OLP board at the receiving end detects that the optical power of the line signals transmitted over the working line fiber is normal. Based on the revertive mode configured on the NMS, the line signals can be switched back to the working line fiber, or still remain in the protection line fiber.